Thomas Willis, (born Jan. 27, 1621, Great Bedwyn, Wiltshire, Eng.—died Nov. 11, 1675, London) British physicians, leader of the English iatrochemists, who attempted to explain the workings of the body from current knowledge of chemical interactions; he is known for his careful studies of the nervous system and of various diseases. An Oxford professor of natural philosophy (1660–75), he opened a London practice in 1666 that became the most fashionable and profitable of the period.

In his Cerebri Anatome, cui accessit Nervorum descriptio et usus (1664; “Anatomy of the Brain, with a Description of the Nerves and Their Function”), the most complete and accurate account of the nervous system to that time, he rendered the first description of the hexagonal continuity of arteries (the circle of Willis) located at the base of the brain and ensuring that organ a maximum blood supply, and of the 11th cranial nerve, or spinal accessory nerve, responsible for motor stimulation of major neck muscles. Willis also was first to describe myasthenia gravis (1671), a chronic muscular fatigue marked by progressive paralysis, and puerperal (childbed) fever, which he named.

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...with the mysticism of the alchemist. A more logical and intelligible view of iatrochemistry was advanced by Franciscus Sylvius, at Leiden, and in England a leading exponent of the same school was Thomas Willis, who is better known for his description of the brain in his Cerebri Anatome Nervorumque Descriptio et Usus (“Anatomy of the Brain and Descriptions and Functions of...